A pioneering essay because this is the first book dealing with this subject at length. The main argument in the book is that the laws of the nida in Islam were designed in contrast to the Jewish ones, in order to differentiate them. The book presents the Islamic legal discourse in detail, and shows the efforts of halachic scholars to create a different halachic system than the Jewish one. The scholars of Islamic law generally dealt with the legal principles and did not enter the details of the Halachot in order to draw conclusions about the manner in which the halacha developed. My research shows the complex discourse of Islamic law and the direction of its development in the most complex field of Islamic law, the laws of niddah.